In Deviations, the main musical material comes from the tensions between natural and tempered harmonic intervals.
The piece is effectively in the key of C. It constantly alternates between notes of the piano, tuned to standard equal temperament, that are flatter than their natural equivalents in just intonation (G, D, Db, Ab, Eb, Gb), and those that are sharper (F, Bb, B, E, A, F#). As a result, each section of the piece uses a limited set of seven notes (the key note C recurs throughout).
I wrote Deviations in rondo form, but it begins with an introduction that draws the listener into the sound world of natural harmonics by activating different harmonics on the C bass strings. After this, the rondo theme is presented in four short phrases (b.10)—two “flat” ones, two “sharp” ones. While each of the three rondo episodes is very different in character and mood, they are all made up of a “flat” and a “sharp” section that uses the corresponding subset of seven notes. The first episode (b.18) is a boisterous dance. The second (b.49) begins with serene, nostalgic melody in three-time and becomes more agitated in the “sharp” section (b.65). The third episode (b.99) is a dialogue between playful and angry phrases, the hands taking turns this time playing the “flat” and “sharp” notes. The delicate closing presentation of the theme (b.134) ends with a simple flourish from the most “out-of-tune” notes to the most “in-tune”.